Treating anode slime from the electrolytic refining of lead.



UNITED STATES PATENT OFFICE.

ANSON GARDNER BETTS, OF TROY, NEW YORK.

TREATING ANODE SLIIEE FROM THE ELECTROLYTIC REFINING OF LEAD.

To all whom it may con cern:

Be it known that I, ANSON GARDNER BETTs. a citizen of the United States, residing at Troy, in the county of Rensselaer and State of New York, have. invented certain new and useful IllllIOVOliKlltS in Treating Anode Slime from the Electrolytic Refining of Lead, of which the following is a specification.

This invention relates to processes of taking metals into solution from the slime withouplprevious drying or fusion.

itherto slime produced in electrolytic lead refineries has been always collected with considerable trouble, and Washed to IQCOVGI the lead depositing electrolyte contained in it, before being submitted to chemical or metallurgical treatment, and even then there is a loss of lead-dc ositing electrolyte.

Some objects 0 my invention are to save the expense in collecting and washing the slime, and at the same time to provide a simpler and more rational treatment than those existing at present.

Other objects will appear in connection with the following description.

I have discovered that I can dissolve both the antimony and lead in the slime, as well as copper, silver and arsenic if desired, by the use of a solution containing an acid makin a soluble lead salt, e. g. fluosilicic acid an also hydrofluoric acid in moderate quantity.

A solution of lead fluosilicicate and fluosilicic acid containing 56% lead and 15% SiF ion I have discovered permits the addition to it of as much as 5% anhydrous HF at a moderate temperature, and considerably more at an elevated tem erature. Such a solution containing 5% H is capable of dissolving 10% antimony as trifluorid, and I havefurther discovered that a solution of antimony trifluorid even in large roportions will not precipitate lead fluorid f rom a lead solution, as the addition of most fluorids, for exam le, sodium fiuorid, will do. I prefer to use, t en, to take the metals of the slime into solution a liquid containing ,considerable fluosilicic acid, and a moderate quantity of hydrofluoric acid.

I have discovered that leadperoxid used in connection with fluosilicic or other equivalent acid will not only cause metallic lead, copper, etc., to go into solution as fluosilicicates, etc. but will also cause antimony to go Specification of Letters Patent.

Application filed January 23, 1907. Serial No. 353,641.

Patented April 20, 1909.

into solution as fiuorid, if hydrofluoric acid is present in a moderate proportion.

As the solution becomes more neutral, the precipitating power for lead of the hydrofluoric acid becomes reater, from the increasing proportion of lead to be precipitated and the decreasing proportion of fluosilicic acid remaining to tend to dissolve any lead fluorid formed. However, the proportion of hydrofluoric acid becomes less, as antimony trifluorid is bein formed, so no lead fluorid is precipitated. iniilar changes take place in a reverse direction in the preferred method of electrolyzing the solution, described below.

Lead peroxid is a powerful oxidizing agent, sufliciently so to cause the formation of silver salts from metallic silver, so I am able to dissolve practically all of such metals of the slime as copper, lead, antimony, tin, silver, and certain amounts of bismuth. However, lead peroxid, especially in the form in which I prefer to produce it, is a slow oxidizing agent, so I prefer to grind it fine before use, and I believe the presence of traces of chromium in the solution act as a catalytic agent and hasten the reaction.

In the practical execution of my process I prefer to proceed as follows: The lead. anodes are suspended in a tank in the usual way with'the usual cathodes, and the whole electrolyzed until the anodes are pretty well dissolved. By suitable means, before or after siphoning the clear solution out of the tank, I cause the slime to drop from the anodes to the bottom of the tank. After removing anode scrap, I then add about the theoretical amount of lead peroxid, necessary to carry out the following reactions:

Pb PbO ?H SiF PbSiF 2H,O Cu PbO 2I-l,SiF PbSiF CuSiF 2Ag PbO 2H SiF Ag SiF PbSiF, 2H 0 2Bi.+ iPbO 6H1? 3H,,SiF,

, 2BiF 3PbSiF (SI-I 0 2As 3PbO 3H SiF,

As,0 3PbSiF 311,0 25b 3PbO 6HF 3H SiF,

2SbF 3PbSiF 6H,,O Sn 2PbO 4HF 2H,SiF,,

SnF 2H,SiF, 41-1 0 The reactions with bismuth and tin are of minor importance as these elements are H SiF solution containing some lead which usually entirely absent or occur in relatively small uantities. The reactions given are those w 'ch I suppose to take place.

The tank is nearly filled with strong may have the composition SiF ion 20%, lead 34%, HF 1 to 2% and stirred preferably until solution is practically complete, or until the slime gets so thin from the solution of its antimony, that it can readil be drawn ofl", which it is difficult to do wit 1 most raw slimes, on account of their heavy nature. The tank is finally cleaned out, and used to refine more lead.

After action is practically complete, the solution, which may contain about 2% antimony, 0.6% arsenic, 1% silver, 1% copper, 18% lead and perhaps 0.1% bismuth, the figures of course subject to great variation, is filtered from gold, and undissolved silver and lead peroxid. The residue is so small in quantity that the loss of fluosilicic acid not washed out is much reduced from the present practice.

I prefer the use of tanks of concrete or cement treated with sulfur as described and claimed in my United States application, Serial Number 346678, filed December 6th, 1906, as being easier to clean and allowing no absorption of solution .containing metals, to afterward difiuse out and render impure lead subsequently deposited in the tank. If the usual wooden tanks are in use, it will be better to remove the slime to special slime treatment tanks, before treatment.

The solution containing the various metals of the slime is led through tanks in which are suspended copper plates, to precipitate out metallic silver. It then passes through a series of electrolytic tanks provided with carbon anodes and suitable cathodes, co per being good for some or all and lead for ot iers, in which a current density is used varying from 5 to 10 or more amperes per square foot with an electromotive force of from 2.2 to 2.5 volts er cell.

Electro ytic copper is deposited on the first cathodes, and continues to deposit until co per is reduced to say 0.1 to 0.2%, when a so 'd alloy of copper and antimony deposits further on in the series of cells, and then impure lead, and then fairly pure lead.

I have found lead peroxld to deposit on the anodes throughout, so that only one anode product is obtained, which is ground and returned to be used in slime treatment.

The cathode deposits are better than expected and are quite satisfactory mechanically. The impure cathodes I prefer to Work up by using them as anodes in a refinery cell, in a series of tanks through which the solution from the slime treatment passes. For example, the copper-antimony cathodes are used as anode and refined by the solutionas it comes from the silver precipitation, copper and antimony going into solution together, while pure copper deposits. In this way a certain amount of these cathodes are always on hand, but do not accumulate faster than they are worked up.

The lead peroxid precipitates as a very hard, smooth conductin coating which warps slightly and drops 0 the anodes occasionally, or can be easily split ofl".

More solution is obtained than was started with, as the slime contained some to start with. Part of the solution should be partially neutralized by treatment with leadv peroxid and lead accordiiig to the reaction Pb PbO 2H Sili ZPbSiF and after being passed through as special electrolytic lead refining cell with lead anodes and cathodes, for the sake of removing any traces of impurities, passed back to the lead depositing plant.

' I may very well also, in treating the slime, use the lead refining solution already in the tank, that is the regular lead refining solution,-for dissolving the metals, provided a certain amount of HF is contained therein or added.

I am not limited to the use of lead peroxid as oxidizing agent. I' can also use for instance, ferric fluosilicate, which, however, does not appear to dissolve silver much in the cold, and other oxidizing salts. The use of lead peroxid, however, is preferred as not involving the use of a diaphragm in the electrolytic cells, and still giving a high current efficiency, and being simpler in other respects.

By the term containing fluorin ion, I mean that the solution contains fluorin in condition which shows the ordinary reaction of fluorin. Thus solutions containing hydrofluoric acid or ammonium fluorid, show the reactions of fluorin; for example, they will precipitate insoluble fiuorids, as lead fluorid, if the conditions of the test are right, while pure fluosilicic acid solution does not contain appreciable quantities of fluorin ion and will not show the tests for fluorin ion. My usage of the term ion is in accord with that of such standard books as Ostwalds Principles of Inorganic Chemistry.

What I claim as new and desire to secure by Letters Patent is:

1. The process of treating anode slime from the electrolytic refining of lead which 2. The process of treating anode slime from the electrolytic refining of lead which consists in dissolving metal therefrom by ing antimony and copper, which consists in treatment Wlth a solution containing fiuorin I dissolving metal therefrom by treatment ion, and with an oxidizing agent, the said so- 1 with lead peroxid and. a solution containing lution also containing relatively strong acid fluorin ion and an acid forming a readilysoluble lead salt, and electrolytically depositforming a soluble lead salt, and recovering metal of the slime from the resulting solution.

3. The process of treating anode slime from the electrolytic refining of lead which consists in dissolving metal therefrom by treatment with a solution containing a considerable amount of the same acid as is con- 3 tained in the electrolyte for refining the lead from which said slime is produced, said soluing antimony from the solution by electrolysis with an insoluble anode and suitable cathode.

6. The process of treating anode slime :1.-

dissolving metal therefrom by treatment with lead peroXid and a solution containing tion also containing fluorin ion, and an oXidizing agent, and recovering metal of the slime from the said solution.

4. The process of treating anode slime from the electrolytic refining of lead which fiuorin ion and an acid forming a readilysoluble load salt and electrolytically depositing copper, antimony and lead successively from the solution, by electrolysis with insoluble anodes, simultaneously depositing consists in dissolving metal therefrom by lead peroXid on the anodes.

treatment with lead peroXid and a solution containing fluorin ion and an acid forming a 1 In testimony whereof I have signed my name to this specification in the presence of readily-soluble lead salt, and electrolytically two subscribing Witnesses.

recoveringlead peroxid and metal of the slime from the resulting solution.

5. The process of treating anode slime from the electrolytic refining of lead contain- ANSON GARDNER BETTS. Witnesses:

SARA A. MALLORY, ETHEL K. BETTS. 

